(1) Technical Field
The present invention relates to display panels that have a plurality of organic light-emitting elements, and in particular to a structure of banks partitioning organic light-emitting elements.
(2) Description of Related Art
In recent years, display panels that have a plurality of organic light-emitting elements are being developed. Among such display panels, there are display panels in which organic light-emitting elements are in sub pixel regions surrounded by column banks and row banks on a substrate. With respect to a height from a top surface of a substrate to top surfaces of the row banks (hereinafter, “row bank height”), it has been proposed to make the row bank height less than a height from the top surface of the substrate to top surfaces of the column banks (hereinafter, “column bank height”) (WO2012/017494A1) and to make the row bank height match the column bank height (JP2009-272081). In any configuration, an organic light-emitting layer included in an organic light-emitting element can be obtained by applying ink containing an organic light-emitting material to a sub pixel region surrounded by column banks and row banks, then drying the ink. Inks containing organic light-emitting materials of different colors are applied to sub pixel regions that are adjacent to each other in a row direction, which is the direction in which the row banks extend, and ink containing organic light-emitting material of the same color is applied to sub pixel regions that are adjacent to each other in a column direction, which is the direction in which the column banks extend.
As shown in WO2012/017494A1, when the row bank height is made lower than the column bank height, ink applied to sub pixel regions that are adjacent to each other in the column direction crosses the row banks and connects. Even if there is a difference in amounts of ink applied to the sub pixel regions that are adjacent to each other in the column direction, the amounts of ink can be equalized. Thus, variation in film thicknesses of organic light-emitting layers that are adjacent to each other in the column direction can be suppressed. Film thickness of an organic light-emitting layer affects properties such as brightness and lifetime of an organic light-emitting element, and therefore suppressing variation in film thicknesses of organic light-emitting layers can suppress variation in properties of organic light-emitting elements. This is not limited to organic light-emitting layers, and as long as a layer constitutes an organic functional layer formed by application of ink, variation in film thickness of the layer can be suppressed, thereby suppressing variation in organic light-emitting elements. Examples of layers that constitute an organic functional layer other than the organic light-emitting layer include a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer. However, when manufacturing a display panel, sometimes a portion of a column bank is unintentionally chipped or foreign matter adheres to a column bank, and therefore a defective portion occurs that makes it impossible for the column bank to block ink flow. When a defective portion occurs in a column bank, inks of different colors applied to sub-pixel regions that are adjacent to each other across the column bank sometimes penetrate through the defective portion. Furthermore, since ink of the same color in the column direction is connected, an ink of a different light-emission color that has penetrated via the defective portion is not limited to only the sub pixel region initially entered, and may penetrate into sub pixel regions that are adjacent in the column direction to the sub pixel region initially entered, and in some cases may further spread to other sub pixel regions in the column direction. In a sub pixel region in which inks of different light-emission colors have entered, an organic light-emitting element display error is caused by ink mixing. Thus, in addition to an organic light-emitting element adjacent to a defective portion of a column bank, display errors also occur in organic light-emitting elements adjacent to the organic light-emitting element.
On the other hand, as shown in JP2009-272081, when the row bank height is made to be equal to the column bank height, ink applied to sub pixel regions that are adjacent in the column direction is blocked by the row banks, and does not connect. Thus, even if an ink of a different light-emission color applied to a sub pixel region that is adjacent across a column bank penetrates through a defective portion, the ink stays in the sub pixel region it enters, and does not spread to other sub pixel regions that are adjacent in the column direction. Thus, organic light-emitting elements in which display errors occur can be limited to only organic light-emitting elements adjacent to the defective portion of the column bank, suppressing a spread of defective organic light-emitting elements due to the defective portion. However, when variation occurs in amounts of ink applied to sub pixel regions that are adjacent in the column direction, ink applied to the sub pixel regions is blocked by the row banks, and therefore equalizing of ink amounts in the sub pixel regions cannot occur, and variation in film thicknesses of organic functional layers that are adjacent in the column direction occurs. Thus, variation occurs in properties such as luminance and lifespan of organic light-emitting elements in the column direction.